Tank cross drive for steering by variable-speed ratio driving means



Feb. 12, 1952 K KELLEY I 2,585,790

TANK CROSS DRIVE FOR STEERING BY VARIABLE-SPEED RATIO DRIVING MEANSFiled April 16, 1945 4 Sheets-Sheet l 8 Q I u w I 3} N x a x J a I l &5?

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Zinnentor BB y W I (Ittorneg Feb. 12,1952 0. K. KELLEY 2,585,790 7 TANKCROSS DRIVE FOR STEERING BY VARIABLE-SPEED RATIO DRIVING MEANS FiledApril 16, 1945 4 SheetsSheet 2 5??? 22% I, w 9; (Iltornegs Feb. 12, 1952K. KELLEY Filed April 16, 1945 O. TANK CROSS DRIVE FOR STEERINGBYVARIABLE-SPEED RATIO DRIVING MEANS 4 Sheets-Sheet 3 (Ittorneg Feb. 12,1952 I O. K. TANK CROSS DRIVE FOR STEERING'BY VARIABLE-SPEED RATIODRIVING MEANS Filed vApril 16, 1945 f4 Sheets-Sheet 4 SECOND ZhwentorKELLEY A 2,585,790

(Itiornegs Patented Feb. 12, 1952 TANK CROSS DRIVE FOR STEERING BYVARIABLE-SPEED RATIO DRIVING MEANS Oliver K. Kelley, Birmingham, MiclL,assignor to General Motors Corporation, Detroit, Mich., a

corporation of Delaware Application April 16, 1945, Serial No. 588,475

1? Claims.

The present invention relates to the drive of large heavy vehicles suchas military tanks, tractors and the like having track laying mechanismcapable of steering by variable speed ratio driving means.

A primary object is to provide a common drive for right and left handtrack drivers, differentially cross-connected for equalization of torqueand speed, and differentially driven by planetary and fluid torqueconverter units arranged to yield a divided torque combined at theoutput differential gearing with controlled reactive steering meanspower driven by the engine.

A further object is to provide a recombined torque at the outputdifferential gearing varying difierentially in accordance with thebraking reaction applied to a power-delivering differential gear unitdriven by the vehicle engine.

A supplementary object is to provide a power transmission fortransmitting one power component to the said output differential gearingfrom said engine at selected variable speed ranges, and a differentialdriving unit for transmitting a second power component from the engineto said output differential gearing such that the net steering effect isvaried in accordance with the driving ratio of the said powertransmission, to produce a faster steering effect when the powertransmission is driving in low gear than when it is driving in higherspeed ratios.

An additional object is to provide a torque dividing and recombiningdriving mechanism which shall have two primary power transmission meansbetween the engine and the first input members of the said outputdifferential gearing for the right and left drives of the vehicle, thetwo said means coupling same selectively through planetary gear andfluid torque converter units for one of the primary torque paths, andthrough planetary gearing for the other of said paths for driving whenthe said first named path is non-driv- Another object is to provide acommon cross drive connecting both right and left output differentialgear units to the outputs of the variable power transmission assembly;and to reversely cross-connect the reaction elements of the said outputdifferential gear units for equalization of both torque and torquereaction in order to establish a self-correcting of torque and speed tostabilize the steering on straight-away driving.

In the customary differentially steered tracklaying vehicle drives,,theuse of step ratio gearing in the drive to the fixed reaction or clutchtypes of output gearing has resulted in a harsh rated by softening theclutching or braking action until accuracy of steering has diminishedbadly and heavy going over rough terrain results in tank drivers losingcontrol, with consequent damage to mechanism and injury to personnel.

Since it is highly desirable that the military track laying vehicleafford a steady gun platform, such vehicles as noted, frequently pitchand jolt so violently that accurate fire beyond 500 yards range iswholly impossible unless the vehicle stop, whereupon it becomes asitting target.

With the present invention, the dynamic power steering mechanism withdifferential compensation means affords a finer and more accuratecontrol of motion which corrects for any sudden force which ifunrestrained would build up a severe lurching moment, and a steadyingeffect of automatic ratio correction by the fluid torque converter, evenwhen the power transmission is changed during a steering action, occursimmediately so as toinduce a graduated torque variation having a netrate of change of low value, controllable by the operator throughmanipulation of the engine throttle and the steering wheel.

Coordinating action of torque compensation occurs at the outputdifferential units, between the primary torque provided by the torqueconverter in all ratios except high gear, and the secondary torqueprovided by the dynamic steering differential mechanism.

Means are provided to release the engine torque at a givenlow enginespeed, combined with means effective to pick up a stalled engine shaftwhen the vehicle has motion either forward or reverse. The automatic,servo operated ratio changing system is supplied by common pump meanswhich assure availability of pressure whenever required.

These advantages among others, make possible the' extension of use ofmilitary vehicles so equipped, so that they may operate successfully inrougher terrain than those not so equipped, as will be understoodfurther herein in detail.

Fig. 1 is a schematic representation of the variable power transmissionassembly for transmitting the primary torque component to the outputdifferential gearing.

Fig. 2 is a similar view representing the power steering mechanism fortransmitting the second:

ary torque component to the output difierential gearing.

Fig. 3 is a wiring diagram for the reaction steering system of Fig. 2.

Fig. 4 is a diagram of the cooling and lubrication system for thebrakes.

Fig. 5 is a speed ratio control diagram for the structure shown in Fig.1.

The diagram of Fig. 1 shows the engine shaft I connected by centrifugalclutch K to gear 3, shaft 1', and driving gear 4, and to the .powershaft 5 of the variable speed transmission assembly. The rotor 53 of thefluid torque converter W is attached to solid shaft 50 and is the outputpower member thereof. Impeller 5|, is driven from hollow shaft 5, andits drum overhangs into the first planetary unit E, having annulus gearteeth 55 meshing with planets 56 spindled on carrier 51 attached topower shaft 5. Reaction sun gear '58 is provided with drum 59 which maybe held against rotation by band 60, for driving the impeller atoverspeed ratio with respect to the engine driven shaft 5. One wayclutch permits rotor 59 to idle when the converter is relieved oftorque, so that the desired steering effect may be maintained on theoverrun.

The converter output shaft 56 extends through hollowshaft and gear 4 tothe opposite side of the centerline of shaft l, and has affixed sun gear62 and carrier 63 as the input power elements for the second planetaryunit F. The output shaft 65 of this unit is affixed to large gear 16 andto carrier 66 for planets 61 meshing externally with reaction annulus'68 and internally with input sun gear 61 the drum 69 of which has twogroups of annular teeth '12 and 13. The annulus '72 meshes with planetsT4 of carrier 15 affixed to shaft 65, and the carrier 63 mounts planets16. The annulus l3 meshes with planets 16 of carrier 63 attached toinput shaft 50 and the planets 16 mesh withreaction sun gear 89 which isattached to drum 8i braked by band 85 for 2nd speed ratio. The drum 99is braked by band 96 for low or first speed ratio. The annulus 68 isbraked by band 95 for reverse gear drive.

v.The planetary unit .G has input annulus ear '86 attached to shaft 5and meshing with planets 81 of output carrier 88 attached to gear 89,and reaction sun gear 9| is braked by band 92.

The cross shaft 26 shown also in Fig. 2., is equipped with gear 96meshing with output gear 10 of planetary unit F, and gear 9'! meshingwith output gear 89 of unit G.

It will'ibe noted that unit G transmits engine torque independently ofunits E, F or W, whereas units E, W and F, drive in series with gear 96of shaft 29.v

For neutral drive, the band 60 of unit E is applied to drum 59 and theother reaction brakes 95, 85 andv 92 are released. The torque convertermay then rotate shaft 56 if the engine throttle is advanced, but nopower be delivered to shaft 2|].

In low'forward, band 66 remains applied, and band 90 of unit F isapplied, stopping drum 69 and annulus 12, so that planets 14 rollaround, driving carrier 15 and shaft 65 of gear in slowly forward, thegear 10 driving gear 96 and shaft 20. This provides a very low ratioforward drive forstarting the motion of the vehicle, the torqueconverter ratio range being superimposed on that of unit F.

For 2nd. speed ratio band .69 remains applied, band 900i unit F isreleased and band 85 applied .to provide reaction by sun gear 80. In

4 this speed ratio unit F yields a compound for ward ratio derived fromthe ratio of gears 13-l68fl superimposed upon that of gears 12-14-452.

The highest gear ratio is obtained through unit G,'by releasing bands.60, or 85, and applying band 92 to establish torque reaction by sungear 9|, to provide reduction drive through the gearing alone. In thisratio, there is a positive, invariable mechanical ratio of drive whereasin low and second, the torque converter in series with unit I gives tworeduction ratio ranges. For normal, fast cross-country driving this willbe the most used ratio, and the torque converter may idle, along withthe trains of unit F.

In reverse, band 50 is applied and band of reverse unit H. This stopsannulus 58 while gear by shaft 65.

ear I9 backwards.

The gear arrangement of groups F and H for compounding for forward andreverse ratios is believed novel. It will be noted that gear group12-'l4-62 is utilized in the compounded 2nd speed ratio as well as inthereverse compound drive with unit H, both of which are driving ratioranges automatically varied by the torque converter W, and by theinitial overspeed ratio of unit E.

In Fig. 2 the engine shaft l drives bevel gear 3 meshing with bevel gear4 of shaft 5 which is the input shaft of the power transmissionassembly. Shaft 29 is driven by the gearing shown, and is attached tothe input sun gears 2| and 2| of the sprocket gear units, for deliveringthe primary torque component thereto.

Each sprocket gear unit consists of differential planetary gearing,input sun gears 2i and 2!, output carriers 23 and 23 afiixedrespectively to and 24. The annulus gears'25 and 25' serve as variablereaction control members for each of the units, as will be understoodfurther.

The bevel gear 6 of shaft 1 is driven reversely at engine speed by gear4. 1

The annulus gears 25 and 25 are toothed externally at 26 and 26' to meshwith gears 28 and 28 respectively, of shafts 30 and 30.

Sleeve 35 rotates freely about shaft 1 and has affixed bevel gear 36meshing with bevel gears 31 and 31 affixed respectively to shafts 3!]and 39.

The variable reaction control gear unit consists of adouble differentialarrangement with the annulus drum 46 attached to shaft I as the powermember, and the sleeve 35 as the load resultant, or driven member.

Planet gears 44 and 44' meshwith annuli 4i and M and with sun ears 45and 45 respectively. a

The engine power provides the second torque component through the gears3., 4, 6 to the steering input power shaft 1 connected to the doubleannulus gear 4l-4,i', meshing with the planets 44-44, which normallyspin on their spindles in the carriers 41 and 41'. The sun gears 45 and45' rotate reversely to drum 40, with their drums 46 and 46'. Carriers4141 are toothed to mesh with bevel gear 43 pivoted on the. casing I00.

The elements 41, 41, shaft 35 and gear 36 are compensating members ofthe differential train. The electric brake B and B act upon drums 46 and46' for steering and braking. Auxiliary bands 48 and 48' are usedforparking the vehicle, and should the electric system fail to function,they are used to brake drums 46 and 46'.for steering and braking.

Without energization, the planets 44-44, sun gears 45-45 and drums 46and 46 idle, but when a drum is retarded, for example drum 46, the sungear 45 will be restrained from further idling, and the carrier 41 willbe driven, where before it was standing still, and forces sleeve 35 andbevel gear 36 to rotate thus causing bevel gears. 31-31 to revolve inopposite directions' This rotation is transmitted by shafts 30-30 andgears 28-28 to the annulus gears -25 of the respective sprocket gearunits, which rotate reversely to each other. This causes the unit outputcarriers 23-23 and sprocket shafts 24-24. to revolve at differentspeeds, hence a steering of the vehicle is achieved by differentialdivided and recombined torque.

If however, drum 41 is freely rotatable and the drum 41 is braked, sungear 45' is retarded, and the bevel gear 43 reverses the hand ofrotation of carrier 41 and sleeve 35, which reverses the relativerotation hands of shafts -30,

so that the annulus 25 which had been as rotating clockwise when viewedfrom beyond the carrier 23 at shaft 24 now rotates counterclockwise. Thedrums 46 and 46 are actually subject to heat from braking effectsderived from the electric brakes B and B and from the application ofbands 48 and 48 therefore the cooling system described further inconnection with Figs. 3 and 4 provides relief of excess heat obtainingfrom both internal and external applications, as will be understoodfurther.

The braking of drum 41 may steer the vehicle to the drivers right and ofdrum 41 cause steering to his left.

With both sets of brakes released, B and B, the cross-connecting gearing36-31-31 between the shafts 30-30 with the annulus gears 25-25 acts as aself-equalizing reaction differential, and the connected elements 26-26,28-28, 30-30, 31-31, gear 36, sleeve 35, and carriers 41 and 41' standstill except for minor hunting caused by variations in tractive eifortresulting from the driving conditions.

This is because of the connecting of their reaction members through thegears 31-31 and 36. Under diiferential traction, this gearing dividesthe tractive effort, which results in rotation of sleeve 35 and thecarriers 41 and 41.

It occurs that the vehicle may be operating under conditions orgradients which cause differential traction, therefore the driver maycorrect any tendency for the vehicle to wander from course, by merelybraking the drums 46 or 46 as required to restore it to the proper lineof motion, and hold it there.

While the entire engine power is delivered by the sun gears 2l-2l whendrive is straight ahead, as soon as either brake B or B is applied, acomponent of engine power derived from bevel gear 6 and shaft 1 isapplied to the annulus gears 25 and 25, so that under unbalancedsteering conditions, the torque is divided proportionally to themagnitude of the braking drum 46 or 46'. At full braking of either drum,the annulus gears 25-25 as shown in the figures herewith revolve atratios with respect to the speeds of the sun.

gears 21-21", soltliat the sprocket shafts revolve reversely at the samespeeds, consequently the vehicle pivots about its own center, to rightor left depending upon the application ofbrake B or B. The steeringmechanism being directly driven by the engine from gear 6 and shaft 1,the steering effect as rate of change of vehicle direction is inaccordance with engine, and, not vehicle speed, therefore in low geardrive by the power transmission, a faster turn will be made than in highgear ratio, for the same engine speed, providing automatic limitation ofturning radius inversely to the variable speed drive ratio.

It is provided that if the vehicle require turning in a restrictedspace, the engine may be throttled below the speed at which torque istransmitted by the power transmission, the steering wheel may be turnedso as to fully brake either of B or B, and the throttle then advanced toexecute the turn on the vehicle center,.being then retarded to halt thespinning motion.

The web |00a of the casing I00 supports the electric brake field coils49 and 49' located radially inward of the drums 46 and 46, and supportsthe spindles of bevel gears 43.

Since under straight forward motion of the vehicle the drums arespinning, conditions are preset for quick generation of retarding forcewhen field coils are excited by closing of their external feed circuits.

Actual experience with this device has been obtained with a 24 voltsystem providing 32 amperes, controlled by a double rheostat with anullcurrent center section for straight steering, and graduated currentcontrol departing therefrom proportional to steering angle, so thatmaximum retardation of the drums at full current occurs.

The circuit diagram of Fig. 3 shows battery M connected to the steeringswitch arm N movable over rheostats R and R, each connected to fieldcoils 49 and 49 for left and right hand braking reaction energizationrespectively, the resistances being diminished with steering angle.

The powerservo circuit shown in Fig. 3 has the battery circuit feed tothe steering contactor passing through contacts l2 and I3 maintained bygovernor U at above a given engine speed, and opened when the governorfalls below that speed. This feature serves the purpose of prevention ofunintentional course movement of the vehicle by steering when the enginemay be idling.

With a small torque value on the output unit sun gears 2l-2I and crossshaft 20, actuation of one of the reaction brakes 46, 46 of the powersteering unit would provide a combined variable torque component on thesprocket shafts 24, 24' compounded from the two sources, but with Iminor reaction braking effect so that the vehicle would move in course,rather than pivot on its own center.

The governor U by withholding servo current from either Winding 49 or 49at below a given engine speed permits the steering control to be set insharp steering position without actuation of the reaction brakes, sothat advancing the engine speed by throttle to a given torque pointpermits the power steering unit and the cross shaft to react to driveone track backward at the same speed as the other drives forward. The

i'iers 23., 23, until engine speed engages centrifugal clutch K.Governor U may be rotated by a driving .connection from one of theshafts 30, 3D or .24. The centrifugal clutch may be of common form suchas is shown for example, in Letters .Patent U. S. 2,162,873 to W. S.Wolfram, issued June 20, 1938. The clutch couples shafts I and I" at agiven speed of shaft I, releasing them at a somewhat lower speed as iscommon in such devices. The freewheel clutch FW is arranged to permitthe flywheel-connected parts to rotate freely during all normal forwarddrive, but to prevent shaft I from rotating forward faster than shaft I.As will be understood, the vehicle may .be towed to start a stalledengine, provided the drive train is adapted to deliver overtaking.torque from the sprocket shafts 24-44 to shaft I.

The diagram of Fig. 4 shows a preferred methed to remove excess brakingheat. A fluid reservoir I5I is connected to the suction of a circulatingpump P which maintains oil pressure for lubrication and servo meansrequired in the vehicle. The braking current circuit when energized,opens valve iGI in the pump pressure line I65, which feeds to line I62delivering the pressure to the brake drum space, from whence it flows bypassage I 63 to cooler I66, and by passage I61 to the reservoir I5I.This method prevents unnecessary withdrawal of oil from the otherutilities, except when needed for lubricating and cooling theelectricallyenergized brake drums and produces instant cooling of theoil upon the energization of the braking circuit. This feature permitspowerful braking of large heavy vehicles and is adapted in drives formilitary tanks, to absorb horsepowers ranging from 1,000 to 2,000 ormore, in accordance with the drive needs.

Operation of Fig. 4 with the control of Fig. 3 is now described. ValveI6! is normally held down by spring I64 seated by collar I68. Boss I1Iblocks outlet port I'IIl connected to line I62, and balanced pressurebetween bosses HI and I12 in port I13 is ready to deliver from inletline I65 whenever port I19 is exposed. 7

Rise of governor contact I3 to connect element I2 and circuit lead I15to battery lead I19 feeds current to switch arm N. With N resting onmid-point I80, no current flows.

When the steering wheel shown in dashed line is moved to cause arm N tocontact resistance R, for example, current flows in lead I to coil 49returning to battery M thru the ground.

Meanwhile the closing of the governor circuit at I2, I3 has permittedcurrent to be delivered thru R, thru lead I14 and lead I18 to the magnetcoil I60 of Fig. 4 for lifting the valve ISI to expose port I10 and feedcoolant to line I62 leading to the passages I8I and I82 of the steeringbrake The coolant feed passage I 8| of Fig. 2 is connected to the mainfeed passage I62 of Fig. 4, and passes thru Web IIlIIa, opening upwardto the space inside drum i6 between the latter and the adjacent fieldI00 of the coil 49. Similarly the coolant feed passage 182 shown at theupper right portion of Fig. 2 leads thru web IIlIla and opens downwardto the similar space inside drum 46 between it and the field I00 of thecoil 49. Passages I81 and I82 may connect to passage I62, and it isobvious that if desired, two separate magnet valves such as shown inFig. 4 mayv bit-individually operated, alternately, for cooling thesteeringbrakes selectively. r

The lead wire I14 from the rhecstatR. 01 Fig. I; is also connected tomagnet valve coil lead wire I18 of Fig. 4 and the lead wire I16 fromrheostat R is connected to the coil thru lead I11. Therefore when eitherof the braking coils 49' or 49 are energised by the steering motion ofcontrol arm N, the coil I60 is energised, valve I6I is opened andcoolant is fed thru passages I62, I8I and I82 to cool the drums '46 and46 of Fig. 2. In the event that selective cooling of one drum at a timeis desired, it is not deemed invention to duplicate the above-describeddisclosure, where found needful. x 7

It should be observed that the cooling requirement for the steeringbrakes B and B, is graduated by the degree of steering angle expressedin angular displacement of the steering control arm N. Sudden, sharpsteering applies full steering braking and also delivers. sufficientcurrent to coil I60 to open the port I1Ilof valve IGI fully and holdsame open. Minor steering motions of short duration cause delivery oflesser coolant volume to line I62. The flooding of the casing sectionsI00, IOila, IOIlb with coolant at other than desired intervals tends todisturb the calculated smoothness of the control, because of fluidturbulence in the brake compartment, therefore a proportionalizing flowcontrol as de scribed above, is effective in a predetermined ratio tothe degree of braking, and cut-ofi occurs when the graduating effect isno longer needed. t is believed of further novelty to arrange thebraking and cooling controls so that the breaking of the governorcontacts I2, I3 at a low speed point likewise interrupts the coolingflow with braking circuit interruption. Otherwise the turbulence effectcould cause irregular drag and steering wander at a time when thevehicle may be in a critical operating position. Exactness of thecontrols is highly desirable. When the emergency steering and parkingbrakes 48 and 48 are used, the construction shown here maybe connectedin the same manner as above described, to energise the circuit of Fig.4, utilizing the principles above taught.

The diagram of Fig. 5 shows the servo operat ing system for controllingthe driving speed ratios of the power transmission assembly of Fig. 1.

The five servo actuators for the reaction brakes 95, 60, 85, and 92 areshown in order from left to right, of the shift sequence.

The motion of the servo pistons to the right is to apply the bands, andto the left to release them.

The servo cylinder 205 houses piston 206; the rod 201 of which is loadedby spring 208 to release the reverse band 95. The springs 2I3, 2I8, 223,and 221 perform the same function for rods 2I2, 2I1, 222 and 226 ofpistons ZII, 2I6, HI and 225 in the cylinders 2 I0, 2 I5, 220 and 224respectively.

The master valve 250 is formed to deliver fluid pressure from the pumpmain 260 between its end bosses a and b. It has five positions markedfrom left to right Rem, Nt, 1, 2, and 3, corresponding to reverse,neutral, low, second and high. For the transitions of low to second andsecond to third, the pressure lines 264 and 268 are branched at 212 and21I to connect to the cylinders H5 and 220 behind the pistons 2H5 and22I.

As shown in the figure, pump pressure is being delivered to cylinder 2I0to push piston 2 to the right and apply brake 60 of Fig. 1. This is theneutral operatingcondition, the control boss 2511c being centered at fN.

It is not deemed necessary to show the pumping system which feeds servopressure main 260. The pump P of Fig. 4 may be of very high volumetriccapacity, and supply line 260; or any arrangement of pumps may be usedwhich assures servo pressure being available such as shown in LettersPatent U. S. 1,523,648 to M. B. Jackson issued January 20, 1925, thisdisclosure providing pressure if the engine is running; or if not, whenthe vehicle is in motion. The pump P of Fig. 4, if so used, for examplemay be driven by auxiliary electric motor or auxiliary combustion enginepower, as is customary in large railcars, airliners, and in marineinstallations for auxiliary power supply. The only safeguard is that thepower be always available when needed to operate the pump and supply thesystem.

Shift of valve 250 one step to the right from .N to 1, retains pressurein cylinder 21!! to hold brake 60 of unit E applied, while deliveringpressure to cylinder 215 to shift piston 2 l6 to the right to applybrake 90 of unit F for drive in low gear.

The next valve step retains pressure in cylinders 2H] and H5, holdingband 60 of unit E locked, but since the rear face of piston 2| 6 ofcylinder 215 is cross-connected to the brake applying pressure incylinder 22!) for the piston 22! which applies brake 85 for 2nd speed,ratio, the admission of pump pressure to the rear of cylinder 2l5equalizes the pressure on piston 216 of cylinder 2 I 5 so that spring 2l8 may retract piston 2| 6 to the left and release brake 96 of unit F,

while the 2nd speed brake 85 is being applied.

Theshift of valve 250 to its full rightward position equalizes thepressure in cylinder 2H1 to release brake 60 of unit E, and theequalized pressure in cylinder 2 I5 is retained to keep band 90released.

The mechanical governor T driven from shaft 5 of Fig. 2 is mounted tocontrol the positioning of a valve 210 which in turn controls the actionof valve 215 located in the path of fluid connection between the outletof valve 250 at line 265 leading by line 268 to the cylinder 224 forcausing piston 225 to apply brake 92 of unit G for high gear drive.

The pressure in line 268 is delivered also to Unit H Unit F Unit G UnitE Brake Brake 90 Brake 85 Brake 92 Brake 60 x 0 0 0 x 0 0 0 0 X 0 x 0 0x 0 0 x 0 x 0 0 O X 0 (The x indicates brake application.)

For all forward driving, brake 66 is applied for the two lowest, andreleased for the highest ratio, and the brakes 90, 85 and 92 are appliedin succession for upshift. It will be observed that i all except high,the gear torque reactions are divided between two brakes.

Clarifying further, the followingpattern of fluid pressure delivery frompump line 260 occurs:

Passages Rev Oonv. Low 2nd High X X X X X (X) X (X) (X) X (The Xindicates pump pressure delivered; the (X) indicates pressure balancedout for unloading the corresponding brake) This governor arrangement ofFig. 5 is novel in that instead of the ordinary overriding manualcontrol applied to the governor, it constitutes a governor controloverriding the manual, serving the purposeof prevention of stalling theengine, overloading the drive, and permitting the driver to devote hisattention to other duties, in handling the vehicle. The governor actionby automatically shifting ratio down likewise improves the steeringeffect, diminishing the turning radius for a given steering wheel anglesetting from normal.

By this, the operator need not concern himself with ordinary crosscountry operation, since it is only necessary after getting the vehicleinto motion, to put the valve in 3 position and forget it, the governoraction plus the automatic ratio drive in the fluid torque converter Wtaking 'care of the drive ratios needed, other than those determinedautomatically by the steering control of Figs. 2 and 3.

The mechanical governor T controlling valve 210 by actuation of its bossor, has only two effective operating conditions, one in which boss bmoves to the right connect 266261 while closing off exhaust port 281,and two, as shown in the figure, whence the line 261 is connected toexhaust port 281 and line 266 is shut off.

Spring 216 may hold valve 215 to the right as shown, in which positionline 268 is open to exhaust between the valve bosses, and feed line 265is cut off.

At a given governor speed, the governor T may shift valve 210 to, theright against spring 282 and connecting lines 266-261, the resultantpressure in 261 shifting valve 215 to the left, connecting feed line 265to line 268 while closing off the exhaust port 214'.

In this condition equalizing pressure is supplied to'cylinders 2H] and220, and actuation pressure to cylinder 224, which releases brakes '60and 85, applying 92.

Now if the governor speeds falls below the desired value for drive inthe high gear ratio, the operator's setting of the valve 250 in position3 for directing pressure to line 265 is annulled by the governorpermitting valve 210 to shift'to the cut-01f position shown. Pressure inspace 219 acting on the end of plunger 290, and aided by leakagetherefrom to the space into which boss b of valve 216 projects, alsotends to hold valve 216 to the left aiding spring 282. The'difierentialareas of bosses a and b may be taken as less than the pressure area ofthe right end area of boss b, for this feature, if needed.

When line 261 is opened to exhaust at 28l, spring 216 shifts valve 215to the right, opening 'line 268 a exhaust at 2 14/ and shutting 268 offfrom feed line 265.

This leaves only brake 920i unit G engaged, for drive in high gear.

The governor valve 210 has the two bosses a and b with a pressure spacebetween them, and the valve casing 300 has four openings in order fromthe left 28I to exhaust; line 261 to relay valve 215'; pump pressureline 265; and pressure relief passage 218 to pump pressure line 266. Be-

7 these lines...

The governor. overcontrol system creates an immediate downshift. to 2ndspeed should the, vehicle speed. drop below a predeterminedmile-perhourfigure, while. the valve 250 is in the high or 3rd position;and it is to. permit shift from 2nd to 3rd only when the speed of thevehicle has reached a given miles per hour.

This control adds maneuvering facility to the control in that the drivermay leave the valve 250 in the highest forward speed radio setting, andproceed, while the governor takes over the work of shifting back andforth between second and high.

In orderto avoid stalling of the engine, overloading of the drive andinadvertent movement of the vehicle in course, caused by steering powerapplied to the drive, the device may be equipped with the,above-described centrifugal clutch K to disconnectthe vehicle enginefrom shaft 1 of Fig. 1, which clutch may be. of common form. Thefreewheel clutch FW idles during all drive by the engine,v but becomes.effective to turn over a stalled engine when the vehicle is towed.

There one advantage derived from the overall dynamic steering systemwhich appears in the maintenance of straight steering by minorcorrections at the. steering wheel. It should be noted that the brakedrums 46, 46 of the power steering unit are constantly spinning when thecompensating gear torque reaction is evenly distributcd, since thecarriers 41, 41' are standing still, and double annulus 4|, 4| is enginedriven.

The instituting of steering brake effect by the power means, starts therelatively inverse rotation of shafts 3.0, 39, and annulus driving gears28, 28. from zero speed, and the addition of the drive component to themtherefore-builds up from.

zero so that whatever the torques are at sun gears 2|, 21. There is agradual superposition of the steering. .component, so gradual that minordirect, travel corrections. by the, steering wheel are made with easeand, without shock, and with, no release and engagement of clutcheshaving different speeds on, their members.

This facility permits full correction for torque differentials, on thesprocket shafts 24, 24 induced by difiicult terrain, so that the vehiclemay actually be steered in a straight line along the curving side of ahill, or with one track in mud, with the other onv a better tractivebase.

The almost instantaneousv response of the power steering device hereinavoids uncertainty of controlwhich heretofore has required operators ofmilitary vehicles in narrow city streets 12 to take the center, to avoidaccidental side-swiping of buildings. A tank,for example, in the middleof a city street is a good artillery target, Whereas if it can hug abuilding line, it is a much poorer target.

These differences are made more apparent by examination of powersteering controls disclosed in the prior art. In Letters Patent U. S.1,387,- 009 to Norelius, a power steering drive is shown in which areoutput planetary gear units having annulus gears driving the sprocketshafts, sun gears driven by engine-driven cross shaft, and the carriersare cross-connected by a compensating gear capable of forward or reverserotation through a friction disc engaged by either one of two frictionrollers, the roller shaft being engine driven. The disc having norotation, while the rollers are spinning, requires that the frictionfaces absorb a severe torque which in practice would cause excessivewear and abrasion whereas the present invention does not have thesedifficulties.

This patented disclosure resemble the friction arrangement of LettersPatent U. S. 1,356,680 to Wickersham, where the output drive is thesame, but which has an engine-driven friction roller which may rotateeither of the reaction carriers normally braked by independent bandbrakes. This has no compensating arrangement, and involves anirreversible connectionwhich in practioe is not believed workable.

Letters Patent U. S. 1,797,797 to Saives shows a power steering unit ofthe planetary gear type, belt-driven by the engine, and arranged todrive a compensating gear connected to drive the sprocket shaftsdirectly through fixed reduction gears. The primary drive is by adifferential unit driven from the engine, having separate reaction sungears braked for normal steering, with a normally disengaged clutch formaintaining the compensating gear inactive. Saives cannot superimposethe torque component of his power steering gear upon that, ofhis primarydrive, nor could he even if the disabling. clutch were left connected,since the locking couples created by the dual differential pattern thuscreated, would prevent the desired steering control.

None of these disclose the principle of applying a power steeringcomponent to the primary drive component derived from a power steeringunit having graduated reaction actuation obtained from a power servosystem directed by the steering wheel. None of these show an outputdifferential having drive reaction taken on compensator-connectedannulus gears such that the primary drive hand of rotation is the sameas that of the output inember. Norelius and Wickersham, noted, haveoutput gear reaction taken on carriers, the input sun gears rotatingreversely to the output annulus gears. In Norelius, for example theoutput carriers stand still when no steering effect is applied, whencethe output sun gears and annulus gears revolve reversely. If the carrieron one side is rotated through the friction gear, so that it moves inthe same direction as the output sun gear, a severe reversal of handofrotation of the output annulus must occur, while the opposite carrier inrotating oppositely to its sun gear ,would cause the correspondingoutput annulus to slow down, these severe torques being referred to thefriction rollers and disc, and to the compensating gear.

The present invention avoids these difficulties by utilizing a form ofoutput gear in which the primary sun gears rotate normally in the same'13 direction as the output carriers, so that a simple and gradualvariation of reaction annulus rotation is obtained by controlledreaction braking in the power differential unit, applied to thecompensating gear.

The presence of the fluid torque converter in the primary path of torqueto the cross shaft and output planetary sun gears provides an extremelyuseful factor in the power steering control, due to the added torquerequirement caused by steering from straightaway, which by increasingthe torque on the converter, reduces the speed ratio, which in turnincreases the steering effect by diminishing the steering radius.

In common tank drives, it is necessary to declutch and shift to a lowerpower transmission gear ratio, for sharp steering, whereas with theinvention herewith, there is an automatic response by the fluid turbinetorque converter which leaves the driver free to carry on other dutiesand focus his attention on the terrain and upon the driving factors.

This effect is enlarged by the action of the governor T shown in Fig.for automatic downshift from high gear at a given low cross shaft speed.Both the torque converter eifect and the governor control thereforeparticipate in this augmented sharp steering action which proceedsautomatically such that when the degree of steering angle is suddenlyincreased, the torque converter will normally reduce speed ratio, and ifthe speed falls off below the limit set for governor T to hold highgear, the valve 215 of Fig. 5 is shifted to release band 92 of the unitG and engage bands 90 and 60 of units F and E.

In actual field tests, the vehicles equipped with this device whensharply steered, turn in a spiral of diminishing radius to a merespinningabout the vehicle center, as for azimuth reconnaissance. Otherdevices do not provide this automatic steering control effect.

Special advantages in the proper distribution of the torques forhandling the heavy reduction load, and in establishing useful ratioranges in sequence are derived from this gear pattern.

The following table of individual ratios by gear units is given by wayof example, for the power transmission gear assembly:

Reverse 0.466 UnitI-l Low 0.388 UnitF' 2nd 1,167 UnitF High 0.641 UnitGThe torque converter W may have a ratio range of from 0.16 to 0.67.

The converter input unit E for example may provide an overspeed of 1.56to l.

The gearing ratio at gears 3, 4 of Fig. 1 may be about 2 to 3, while thenormal reduction range of the output differential units which drive thesprocket shafts 24, 24, may be approximately 4 to 1.

One skilled in the art will observe that in this demonstration anoverall gear reduction of about With the available spread of ratiofactors it is therefore possible to operate the fluidtorque converterwithin its most efficient ratio range, which adds to the performance ofthe vehicle.

The automatic ratio changing response of the fluid torque converter overits effective reduction ratio range is effectively utilized to assiststeering as will be understood from the foregoing description. w

It is-not deemed necessary to repeat the drive operating descriptiongiven above for the pres-' ent' invention, in that it should be obviousto one skilled in the art how this device is controlled.

Reference has been made herewith to certain selections from the priorart in order to set apart clearly, the present invention from the priorart. It is believed well demonstrated that the advantages set forth inthe preliminary paragraphs of this specification are here amplydemonstrated.

Although the applicant has described one particular physical embodimentof his invention, and explained the operation, the construction, andprinciples thereof; it should be understood that the form of theinvention shown is merely by way of illustration and that other formsutilizin the invention may be designed without departing from the spiritor essential characteristics thereof, the scope of theinventiondisclosed herein being outlined in the appended claims.

The applicant therefore desires to obtain by Letters Patent thefollowing claimed invention.

1. In a track laying vehicle, an engine, a variable power transmissiondriven by said engine and adapted to drive laterally disposed gearingunits coupled to track laying and driving mechanism, power steeringmeans driven by said engine and adapted to transmit driving power tosaid units, reaction elements of said means individually operable todirect and control the power of said steering means, servo power meansoperable to actuate said elements, and control mechanism for said servopower means effective to select and graduate the application of power tosaid reaction elements for steering the vehicle.

2. 'In a track laying vehicle drive, an engine, a power transmission,final drive differential gear units laterally disposed for drivinglaterally placed tracks, said units each having input, output andreaction members, a power steering differential gear unit; acompensating gear coupling the said reaction members and driven by 'saidsteering differentialgear unit, a primary driven shaft driven by saidpower transmission and transmitting a primary power component to theinput members of said differential units, a secondary driving shaftdriven by said engine and driving said steering differential gear unit,braking means for said steering differential gear unit, servo meansadapted to actuate said braking means, and a steering control means forsaid servo means having a mid-position in which the said servo means isinactive while said compensating gear coupling equalizes the reactiontorque between said reaction members for straight for ward steering, andhaving right and left steering positions in which thesaid servo meansactuates the said braking means for causing the steering differentialgear unit to drive the said compensating gear to apply forward drivingpower to one or the other of said final drive unit reaction members.

3. In combined driving and steering mechanism for track-laying vehicle,a power drive meanscomprising track-driving mechanisms lat- 15 erally'disposed to the normal direction of motion of the vehicle, each having adifferential gear unit including an output member, a primary inputmember and a, third member normally acting as the reaction supportingelement of said unit, a cross shaft connecting the primary input membersto drive at unit speed, an engine, a variable ratio power transmissiondriven by said engine and geared to drive said cross shaft, a

compensating gear device coupling the said third members of saidmechanisms so that variations of the torques delivered by said units areequal- 'ized, a driving shaft for said device, a driveroperated steeringmeans, a steering differential gear driven by'said engine and connectedto said driving shaft, said steering differential gear having brakingmeans individually operable to compel said driving shaft to rotate inone dil'GClllOlb or the opposite direction, and control means for saidbraking means operated by said steering means and eifective to graduatethe operation of said braking means so that an increased braking meansaction provides an accelerated rate of change of rotation from zerospeed of said driving shaft in either direction of rotation.

4. In a vehicle driven by a track laying drive mechanism having finaldrive wheels, an engine, a power transmission driven by said engine, apower steering means driven by said engine and including reaction brakesindividually operable. output differential gearing for each of saidfinal drive wheels, each gearing being drivable at variable speed bysaid power transmission and each having a reaction element drivableforward-1y and reversely by said power steering means, andoperator-controlled means effective to select and to graduate theapplication of said brakes for varying the rotation of said reactionelements driven by said power steering means and thereby vary therelative speeds of rotation I ofsaid wheels simultaneously for steeringthe said vehicle.

5; In a vehicle driven by a track laying mechanism having final drivewheels, an engine, a

power transmission driven by said engine. a power steering means forsaid vehicle including selectively operable reaction brakes, a powerconnection to drive said means from said engine, output differentialgearing for each of said final drive wheels, each gearing being drivableat variable speed by said power transmission and each having a reactionelement drivable forwardly and reversely by said power steering means,op-

erator-controlled steering means effective to select and to graduate theapplication of said brakes v for varying the rotation of said reactionelements driven by said power steering means to vary the relativerotation of said wheels, and operatorcontrolled means operative tochange the driving ratio of said power transmission for varying the rateof change of the steering effect determined by said steering means.

6. In the combination set forth in claim 1, the sub-combination of asteering device for said control mechanism and a second set of reactioncontrolling means operable upon said elements and operated independentlyof said device for the purpose of furnishing steering control when thesaid servo power means fails to respond to said control mechanism.

7. In the combination set forth in claim 1, the sub-combination of an.electrical power source forv said servo power meansv and of. acurrentvarying apparatus operated by said control mechanism to vary theaction of said servo power means.

'8. In a vehicle equipped with a track laying drive, an engine, anengine shaft, a power steering differential gear unit having an input.shaft concentric with said engine shaft and a. concentric power deliveryshaft, a compensating gear unit driven by said power delivery shaft,laterally disposed track-laying mechanisms, separate final drivedifferential gear units for each said mechanism, input and reactionmembers for said differential units, a cross shaftconnected to drive theinput members of said units, a power transmission assembly arranged.parallel to-said cross shaft and coupled thereto by gearing, a torquedividing bevel gear driven by said engine shaft and driving saidassembly and said input shaft for the power steering differential gearunit, and concentric reaction control shafts laterally geared to saidreaction members with each connected to a bevel gear of saidcompensating gear unit meshed with a bevel gear affixed to the outputshaft of said steering differential gear unit.

9. In steering, controls for track laying vehicles, a variable speeddrive mechanism adapted to drive laterally disposed tracks atdifferential forward and reverse. speeds including output differ: entialgearing connected to drive said tracks and ediiipped with reactionelements adapted to be driven at variable speed ratios, a continuouslyvariable power transmission assemblyincluding,

step-ratio gearing for driving said output differential gearing, anengine, a steering differential gear operable to drive said reactionelements at variable speed ratios and a common driving gear :onnectingsaid engine to both said power transnission and said steeringdifferential gear.

10. In a track laying vehicle, an engine, a variable power transmission.including a hydraulic torque converter driven by said engine and adaptedto drive laterally disposed gearing units coupled to track laying anddriving mechanism, power steering means driven by said engine andadaptedto transmit driving power to said units, reaction elementsindividually energisable to direct and control the power of saidsteering means, servo power means operable to energise said elements,and control mechanism for said servo power means effective to select andgraduate the application of power to said reaction elements for steeringthe vehicle.

11. In a track laying vehicle drive, an engine, a power transmission,including a continuously variable fluid torque converter, final drivedifferential gear units laterally disposed for driving laterally placedtracks, said units each having input, output and reaction members, apower steering differential gear unit, a compensating gear coupling thesaid reaction members and driven by said steering differential gearunit, a primary driven shaft driven by said power trans mission andtransmitting a primary power component to the input members of saiddifierential units, a secondary driving shaft driven by said engine anddriving steering differential gear unit, braking means for said steeringdifferential gear unit, servo means adapted to actuate said brakingmeans, and a steering control means for said servo means having amidposition in. which the said servo means is inactive while saidcompensating gear coupling equalizes the reaction torque between saidreaction members for straight forward steering, and having right andleft steering positions in which the said servo means actuates the saidbraking means for causing the steering differential gear unit to drivethe said compensating gear to apply forward driving power to one or theother of said final drive unit reaction members.

12. In combined driving and steering mechanism for track-laying vehicle,a power drive means comprising track-driving mechanisms laterallydisposed to the normal direction of motion of the vehicle, each having adifferential gear unit including an output member, a primary inputmember and a third member normally acting as the reaction supportingelement of said unit, a cross shaft connecting the primary input membersto drive at unit speed, an engine, a variable ratio power transmissionincluding a fluid turbine torque converter driven by said engine andgeared to drive said cross shaft, a compensating gear device couplingthe said third members of laterally disposed units so that variations ofthe torques delivered by said units are equalized, a driving shaft forsaid device, a driver-operated steering means, a steering. differentialgear driven by said engine and connected to said driving shaft, saidsteering differential gear having braking means individually operable tocompel said driving shaft to rotate in one direction or the oppositedirection, and control means for said braking means operated by saidsteering means and efiective to graduate the operation of said brakingmeans so that an increased braking means action provides an acceleratedrate of change of rotation from zero speed of said driving shaft ineither direction of rotation.

13. In a vehicle driven by a track laying drive mechanism having finaldrive wheels, an engine, 7

a power transmission having a continuously variable fiuid turbine torqueconverter in the driving train driven by said engine, a power steeringmeans driven by said engine and including reaction brakes individuallyoperable, output differential gearing for each of said final drivewheels, each gearing being drivable at variable speeds by said powertransmission and each having a reaction element drivable forwardly andreversely by said power steering means, and operator-controlled meansefiective to select and to graduate the application of said brakes forvarying the rotation of said reaction elements driven by said powersteering means and thereby vary the relative speeds of rotation of saidwheels simultaneously for steering the said vehicle.

14. In the combination set forth in claim 1 in which the controlmechanism for said servo power means is operator-controlled, thesubcombination of a second set of steering reaction control meansoperable upon said elements, means independent of saidoperator-controlled means for energizing said second set of reactioncontrol means when the said servo power means fails to respond to saidoperator-controlled means, and a further control means efiective tointerrupt the action of said operator-controlled means, said furthercontrol means responding to speed.

15. Driving and steering mechanism for track laying vehicles comprisingin combination a pair of track driving sprockets; a differentia1 gearingunit for driving each sprocket, each unit including a rotary drivingelement, a rotary reaction element, and a driven element rotated by thecombined movement of the driving element and reaction element; thedriven element of each unit driving a sprocket; an engine; a changespeed driving connection between the engine and both driving elementsfor driving both driving elements in one direction and at the samespeed; means for changing the speed ratio of said driving connection;differential steering gearing driven by the engine and connected todrive said reaction elements simultaneously in opposite directions todrive each sprocket at a speed which is the algebraic resultant of thespeeds of the driving element and the reaction element of its associatedunit.

16. Driving and steering mechanism for track laying vehicles comprisingin combination a pair of track driving sprockets; a differential gearingunit for driving each sprocket, each unit including a rotary drivingelement, a rotary reaction element, and a driven element rotated by thecombined movement of the driving element and reaction element; thedriven element of each unit driving a sprocket; an engine; a powertransmission assembly driven by the engine and driving both said drivingelements; the assembly including means for changing the ratio of torquesupplied-by the engine to that of the torque delivered to the drivingelements while transmitting torque continuously to the driving elements;steering differential gearing driven by the engine independently of saidpower transmission assembly and operative to drive the two reactionelements in opposite directions simultaneously whereby one track isdriven faster than the other track by said driven elements.

17. In a track laying vehicle, a variable speed drive apparatus arrangedto drive laterally disposed tracks at differential forward and reversespeeds including output differential gear units connected to drive saidtracks, each said unit including a variable speed reaction element, thedrive apparatus also including a continuously variable powertransmission combined with step ratio gearing and constantly connectedto drive said units, an engine driving said power transmission, asteering differential gearing also driven by said engine and acompensating gear driven by said differential gearing and connected todrive said reaction elements at varying speeds, and a control device forsaid steering differential gearing effective to establish faster andslower relative speeds of said tracks by varying the speed of saidcompensating gear.

OLIVER K. KELLEY.

REFERENCES CITED I The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,247,725 Schneider Nov. 27 19171,387,009 Norelius Aug. 9, 1921 1,688,643 Murfey et a1 Oct. 23, 19281,797,797 Saives Mar. 24, 1931 2,272,934 Cotal Feb. 10, 1942 2,297,162Olcott Sept. 29, 1942 2,336,912 Zimmermann Dec. 14, 1943 2,355,484 TekerAug. 8, 1944 2,386,701 Martin Oct. 9, 1945 2,523,766 Kelley Sept. 26,1950 FOREIGN PATENTS Number Country Date 312,527 Great Britain May 30,1929

